1. Field of the Invention
The present invention relates to a zoom lens system which is utilized in a photographic camera, especially a lens-shutter type camera with a wide angle range (e.g., a half angle-of-view of more than 40°) and a zoom ratio (magnification ratio) of more than 3.5.
2. Description of the Prior Art
A zoom lens system of a compact camera does not require a long back focal distance, unlike a zoom lens system of a single lens reflex (SLR) camera which requires a space to provide a mirror behind the photographing lens system. Therefore in a compact camera, a telephoto-type lens system, including a positive lens group and a negative lens group, in this order from the object, is generally used. On the other hand, in a single lens reflex camera, a retrofocus-type lens system, including a negative lens group and a positive lens group, in this order from the object, is generally used.
In such a telephoto-type lens system (the “positive-lead” lens system) in which the positive lens group is provided closer to the object than the negative lens group is, miniaturization of the lens system can be easily made; however, it is difficult to make the focal length shorter at the short focal length extremity, i.e., the difficulty in achieving a wide angle of view.
In order to overcome the above-described drawbacks, a zoom lens system of three-lens-group arrangement (a negative lens group, a positive lens group, and a negative lens group) has been proposed for the purpose of making the focal length at the short focal length extremity shorter in, e.g., Japanese Unexamined Patent Publication Nos. Hei-5-93865 and Hei-6-82697. According to such a “negative-lead” lens system, it is easy to make the focal length at the short focal length extremity shorter; however, it is difficult to achieve a high zoom ratio; and the frontmost lens diameter tends to become larger. Accordingly, if such a zoom lens system is employed in a telescoping-retractable zoom lens system having a plurality of lens barrels, the entire camera becomes large, since the frontmost lens diameter is, as explained, larger. Moreover, if an attempt is made to increase the zoom ratio thereof, the overall length of the zoom lens system at the long focal length extremity becomes longer.